There was no immediate reports of casualties nor was it clear how many assailants had penetrated PAF Base Minhas, in the town of Kamra in Punjab province, about 80 kilometres northwest of Islamabad.
An air force statement said forces had cordoned off the area around the air base.
Police officer Hafeez Aulakh said the militants entered the air base before dawn on Thursday. He was standing outside the air base and could hear intense gunfire and see flames leaping up from inside.
Officials said special forces were scrambled to respond to the attack at the base, home to the Pakistan Aeronautical Complex, the manufacturing division of the air force that builds Mirage and, with Chinese support, JF-17 fighter jets.

Witnesses said they could hear gun and rocket fire, and the sound of hand grenades coming from the facility.
"A group of terrorists has attacked a portion of PAF Base Minhas," the Pakistan Air Force announced in a brief statement.
"Intense fire is being exchanged between the security personnel and the terrorists," it added without giving any further information.
There was no immediate claim of responsibility but Islamist militants linked to the Pakistani Taliban have targeted a string of military bases in a five-year insurgency.
In May 2011, it took security forces 17 hours to quell a similar attack on an air base in the southern city of Karachi that killed 10 security personnel and destroyed two US-made aircraft, and was claimed by the Taliban.
The military in Kamra, in the central province of Punjab, has been targeted at least twice in recent years.
On October 23, 2009 a suicide bomber killed six civilians and two Pakistan Air Force personnel at a checkpoint outside the base during morning rush hour.
On December 10, 2007, a suicide car bomber struck a school bus, wounding at least five children of base employees.